1. Field of the Invention
The invention relates to an operational amplifier, and is applicable to, for example, an operational amplifier applicable to a preamplifier, a premain amp, and the like in an audio system.
2. Description of the Background Art
A conventional IC-compatible operational amplifier is mentioned in Reference 1 (“Semiconductor Introductory Course 2 Semiconductor circuit II by program learning”, written and edited by Vocational Training Development Textbook Committee, and published by KOSAIDO PUBLISHING, PP. 179-181.) The configuration of the operational amplifier mentioned in Reference 1 is basic configuration that is adopted in 072-series operational amplifiers sold by various companies.
The operational amplifier mentioned in Reference 1 has: as shown in FIG. 4, a differential amplifier that converts into a current signal a difference voltage (input voltage) between an input potential to a non-inverting input terminal (+ input terminal) and an input potential to an inverting input terminal (− input terminal); an emitter follower that converts, into a voltage signal, the current signal obtained by the conversion; a grounded-emitter amplifier that amplifies the output voltage from the emitter follower; and a power amplifier that outputs, to an output terminal, the output voltage signal from the grounded-emitter amplifier.
However, the conventional operational amplifier suffers from the following problems.
First, the conventional operational amplifier has a large number of transistors suffering from a problem with the parasitic capacity between a base and a collector (Miller effect), thus resulting in a narrow band applicable to the operational amplifier.
Secondly, due to the presence of a large number of transistors suffering from the Miller effect problem, the maximum phase rotation of an output signal with respect to an input in the operational amplifier exceeds 180 degrees, thus causing a risk of oscillation in application of this operational amplifier with an additional negative feedback path.
Thirdly, due to the presence of a large number of transistors suffering from the Miller effect problem, large disturbing noise is generated.